A majority of children worldwide learn more than one language (Grosjean, 2010), yet theories of language acquisition treat monolingualism as the standard learning model. Bilingualism is highly common, but the mechanisms that drive bilingual learning are not yet well understood. In order to develop rich theories of language acquisition, it is necessary to include a full consideration of the demands of bilingual learning environments and how learners cope with these demands. The proposed research project seeks to fill this theoretical gap by investigating bilingual statistical learning at the very early stages of languag acquisition. Statistical learning entails discovering structure by tracking patterns that are preset in the input. Statistical learning is a popular framework that has received a great deal of attention for its potential to explain how infants and children acquire many dimensions of linguistic structure. Infants are remarkably skilled at tracking regularities. However, the literatre has not yet addressed how bilingualism affects the ability to extract statistical regularities in linguistic input. The demands are substantially greater for bilinguals than for monolinguals. They must track two separate sets of regularities for every aspect of linguistic structure, from sounds to words to grammar. This research will examine two processes that are fundamental for early language acquisition, the ability to detect words in fluent speech and the ability to associate word forms with meanings. The experiments will address how dual language input affects infants' ability to perform these tasks. In addition, both monolingual and bilingual infants will participate, providing a window on how bilingual experience affects infants' tracking of regularities in dual languages. The project will also explore what cognitive processes support bilingual infants' ability to learn effectively in two immensely complex linguistic systems, focusig on how cognitive control and vocabulary composition relate to statistical learning skills in the laboratory. In addressing a theoretical gap, the proposed research also has substantial significance for public health. This work will reveal mechanisms that infants use to learn and the conditions that support or hinder bilingual learning. These contributions have potential to affect the design and implementation of early bilingual education programs. In addition, this work will elucidate the mechanisms that typically developing infants use to acquire language, which has applied value for the study of language impairments. Understanding the underlying processes of typical development is crucial for understanding the development of populations who are not acquiring language on a typical course. It is important to know how learning typically proceeds in order to identify potential underlying deficits in learning impairments.